EDIT: Forgot to mention that I don't have any special medical knowledge or experience. Going off of what I've found on Wikipedia + a paper.
One of the nice things about tianeptine in comparison to other antidepressants is that it's rapidly evacuated from the body (half life's 2.5 hours according to Wikipedia). If you want to roll, it's likely that you'll only have to discontinue use of your antidepressant for a short while (e.g. a day or two) rather than 1-3 months like you would on Prozac. Another nice thing about it is that it doesn't occupy cytochrome P450, which is used in MDMA's main metabolic pathway...a lot of other drugs do, which tends to make both drugs' pharmacokinetics a little messed up.
Standard disclaimer applies: if you're clinically depressed, you may want to avoid MDMA because it might make your condition worse. Discontinuing your antidepressant medication in order to roll may also have negative consequences.
As for what would happen if you took tianeptine and MDMA at the same time...my assumption (based on nothing but Wikipedia's pages on Tianeptine and SSREs) is that it wouldn't significantly affect your roll. Tianeptine activates glutamate receptors to indirectly cause SERT to be more efficient rather than binding to SERT directly. This means there's no competition between MDMA and tianeptine at SERT: MDMA can reverse SERT and pump serotonin into your brain as it normally does. Tianeptine works as an antidepressant by raising the relative level of dopamine compared to serotonin, so it's likely that MDMA will block its antidepressant effect by raising serotonin levels. Then again, you'll be rolling, so you probably won't notice this. *shrug*
Once again, just a theory, and one that you can review against Wikipedia with ease.
For your convenience (Wiki links):
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Tianeptine
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SSRE